Catalyst for the alkaline-catalyzed polymerization of pyrrolidone is usually made by adding an alkali metal hydroxide to excess 2-pyrrolidone. The subsequent reaction produces the alkali metal pyrrolidonate catalyst and water. In order to effectively carry out polymerization, the water should be promptly removed. Its removal is accomplished by heating the mixture at least up to incipient distillation of 2-pyrrolidone (90.degree.-110.degree. C) under reduced pressure (1-10 torr). Preferably, an appreciable amount of 2-pyrrolidone is distilled out to ensure substantially anhydrous polymerization conditions (see U.S. Pat. No. 3,721,652).
The catalyst may also be prepared by contacting an alkali metal alkoxide with excess 2-pyrrolidone and distilling off the product alcohol. For example, 2-pyrrolidone is contacted with the alkali metal alkoxide in excess alcohol and then the alcohol is distilled off under reduced pressure (see U.S. Pat. No. 2,727,017); however, this produces poor-quality (low-assay) sodium pyrrolidonate (see U.S. Pat. No. 3,346,566). More efficiently, the alcohol is removed by adding an inert liquid, such as benzene, which forms an azeotrope with the alcohol and then performing an azeotropic distillation.
2-PYRROLIDONE IS COMPLETELY MISCIBLE WITH WATER AND ALCOHOL, AND THESE SOLVENTS ARE NOT EASILY REMOVED FROM PYRROLIDONE. Consequently, azeotropic distillation and/or distillation under vacuum have heretofore been used to remove the alcohol or water which is a by-product of catalyst preparation. However, these distillation methods are inefficiently adapted to large-scale production of catalyst.